The present invention relates to curing of isocyanates in the presence of amino catalysts and more particularly to the novel use of ortho carboxylic acid esters as co-catalysts therefor.
Quaternary ammonium salts are known to be efficient trimerization catalysts and are known to be effective in making isocyanurate-type polyisocyanates. Trimerization of isocyanates into isocyanurates is a reaction that can be continued for formation of coatings, adhesives, elastomers and plastics, and like products. The trimerization reaction usually requires some heat even in the presence of quaternary ammonium catalysts.
The predominant form of the quaternary ammonium catalyst comprises quaternary ammonium hydroxide salts as proposed by German Pat. No. 1,150,080. U.S. Pat. No. 3,487,080 proposes trimerization of isocyanates in the presence of quaternary ammonium hydroxides plus a compound selected from a phenol, an oxime, or methanol. U.S. Pat. No. 4,040,992 conducts the trimerization reaction utilizing shortened carboxylic acid salts of quaternary ammonium hydroxyl compounds. U.S. Pat. No. 3,179,626 proposes the use of tertiary amines in combination with aldehydes in the preparation of polyurethanes, polyisocyanurates, and polyureas.
In some uses such as structural foams and reaction injection moldings (RIM polyurethanes), it is desired that the catalyst system exhibit a controlled induction period. That is, the curable composition should have a specified period of time during which virtually no viscosity increase is evident. This permits the composition to be placed in a mold or penetrate through reinforcement fiber and adequately wet the fiber, for example, prior to the composition reaching its gel point and curing. Once the gel point has been reached, however, cure should be fairly rapid. The use of acids, for example, as noted above is one method for achieving the delay in cure of the curable composition.